The statements in this section merely provide background information related to the present disclosure and do not necessarily constitute prior art.
A power amplifier is an essential part for transmitting a signal in a communication system. In general, the power amplifier is driven in a low-power level to operate with linear characteristics instead of being driven in a saturated level with much nonlinear characteristics, considering signal quality and interference with a neighboring band. However, if the power amplifier is driven with a power lower than the saturated power, the efficiency of the power amplifier is lowered by about 10% to 20%.
The digital pre-distortion (PDP), which is one of the linearization techniques to improve the efficiency of the power amplifier, is getting an attention as an effective technique that can be achieved with simple structure and low cost. Specifically, the digital pre-distortion linearizes a nonlinear power amplifier by obtaining digital pre-distortion characteristics corresponding to an inverse function of the nonlinear power amplifier and applying the digital pre-distortion characteristics to an inpuit signal.
Characteristics of the power amplifier tend to vary with time, power and temperature, and hence the corresponding inverse function is to be obtained by continuously tracking the nonlinear characteristics. To this end, the digital pre-distortion amplifier calculates a pre-distortion parameter for applying the pre-distortion to the signal inputted to the power amplifier from the transmission signal and the output signal outputted from the preamplifier.
The digital pre-distortion apparatus calculates the pre-distortion parameter by using a plurality of samples acquired from a transmission signal, and hence in order to obtain an accurate pre-distortion parameter, a sufficiently large number of samples having various signal amplitudes are needed. However, the more samples need the more capacity of a memory, which increases the load of the hardware and also increases the cost.
Even when a sufficiently large number of samples are collected using a large-capacity memory, if some inappropriate samples are included in the collected samples, it may be hard to obtain accurate pre-distortion characteristics due to an error caused by the inappropriate samples. For example, when the signal is a time division duplex (TDD) signal, there is a risk that samples having no signal are included in the collected samples.